The present invention relates generally to seals in a turbine for sealing between stationary and rotating components thereof and particularly relates to a hybrid brush/honeycomb seal combination for sealing between high and low pressure regions about a turbine steam gland.
Various type of seals are employed in a turbine between rotary and stationary components or between stationary components. For example, brush seals have been interposed between a stationary component and a rotary component. As well known, brush seals include a plurality of bristles disposed in a support with bristle tips projecting from the support for engagement with the rotary component. While brush seals per se are highly useful in this context, brush seals are incapable of withstanding high pressure differentials, for example, those found between high and low pressure regions on opposite sides of a steam gland in a turbine.
Labyrinth-type seals are often employed in turbines for sealing between stationary and rotary components. Because of the need to space the labyrinth teeth from the rotary component, labyrinth type seals demonstrate less than optimum leakage performance as well as the potential for heat induced damage to the rotor should the labyrinth seal teeth rub against the rotor. Honeycomb seals are also sometimes employed to seal between stationary and rotary components in turbines. While honeycomb seals typically negate the problem of heat induced damage to the rotor in comparison with labyrinth type seals, honeycomb seals provide only a marginal improvement in leakage performance when compared to labyrinth seals. Further, where substantial pressure differences exist between high and low pressure regions in the turbine, axially spaced brush seals do not function to share the pressure differential and would not meet the sealing requirements between these high and low pressure regions. Consequently, there is a need for a seal having improved leakage performance and which has the capability of sealing between high and low pressure regions with very substantial pressure differentials therebetween while at the same time minimizing the potential for heat induced damage to the rotor.
In accordance with a preferred embodiment of the present invention, there is provided a hybrid seal for sealing between a rotary component and a stationary component including a seal body carrying arcuate first and second axially spaced brush seals about a rotary component. The seal also includes an arcuate honeycomb seal structure between the axially spaced brush seals. The honeycomb seal includes a plurality of channels extending generally radially and opening towards the rotary component. The hybrid seal including the brush seal/honeycomb combination carried by a single seal body minimizes the possibility of heat induced damage to the rotor with improved leakage performance by minimizing air and steam leakage between high and low pressure regions having a substantial pressure difference.
In a specific application of the hybrid seal hereof, the seal is formed in a steam gland in a turbine. The steam gland seals, for example, between a high pressure inlet scroll which supplies steam for transmission at high pressure to turbine buckets to cool the buckets and a low pressure steam leakage extraction scroll. The steam gland includes an outer shell defining the steam inlet and extraction scrolls, the scrolls being axially separated from one another by an elongated dovetail-shaped groove. The hybrid seal includes a generally annular seal body formed of arcuate seal segments disposed in the groove. Each segment mounts a pair of axially spaced brush seals and a honeycomb seal intermediate the brush seals. This sequential arrangement of brush seals and honeycomb seals achieves a balanced sharing of the pressure differential between the high pressure steam inlet scroll and the low pressure steam extraction scroll. A plurality of segments are provided in the dovetail groove in each of the upper and lower shells forming the turbine casing and steam gland, registering adjacent ends of the segments having a spline seal sealing between the segments. The segmented seals thus utilize intersegment spline seals to minimize end leakage.
In a preferred embodiment hereof, there is provided a seal for sealing between a rotary component and a stationary component comprising a seal body carried by the stationary component and carrying first and second arcuate brush seals. Each brush seal includes a support and a plurality of bristles carried by the support. Tips of the bristles extend beyond said support for engaging the rotary component. The brush seals are spaced axially from one another. The seal body carries an arcuate honeycomb seal extending circumferentially and axially between the first and second brush seals, the honeycomb seal including a plurality of generally radial channels opening toward the rotary component whereby the brush and honeycomb seals seal between axially spaced high and low pressure regions on axially opposite sides of the seal.
In a further preferred embodiment hereof, there is provided a steam gland in a turbine comprising a stationary casing having a generally annular steam inlet scroll and a generally annular steam extraction scroll axially spaced from one another, a rotary component within the stationary component, a seal between the inlet scroll and the extraction scroll sealing between the stationary and rotary components and high and low pressure regions on opposite sides of the seal, a seal body carried by the stationary component and carrying first and second arcuate brush seals, each brush seal including a support and a plurality of bristles carried by the support with tips of the bristles extending beyond the support for engaging the rotary component, the brush seals being spaced axially from one another, the seal body including an arcuate honeycomb seal extending axially between the first and second brush seals, the honeycomb seal including a plurality of generally radial channels opening toward the rotary component whereby said brush and honeycomb seals seal between axially spaced high and low pressure regions on axially opposite sides of the seal.